Driving emissives with mesh objests
Here is a gross way to do it. Unfortunately I couldn't use the NLA with the node actions which would have made it simpler, either I miss something or Blender doesn't manage node actions like other actions:

Create 4 spheres within one single object, unwrap with Project From View, build the following node setup, basically a ColorRamp is used to manage a transition between a blue emission and transparency, I made the setup a bit more complex as I wanted a bit of Layer Weight. At frame 0 set the Mapping Location value in order to make the object completely transparent, keyframe the value:



At frame X, change the Location value so that the sphere are now completely lit:



select the object and press AltD to link-duplicate, move the duplication, rotate it, duplicate it again to create a whole triangle. Also duplicate the material and change the Mapping Location values in order to delay the light: